During vascular surgery or endovascular treatment of vessels including atherectomy, balloon angioplasty, and/or stent deployment, debris such as plaque and blood clots can move from the treatment site through a vein or artery, thus compromising the flow of blood at a location distal from the treatment site. Various distal protection systems have been developed to prevent such debris from embolizing in the vessel. Such distal protection devices include filters and occlusive devices. (e.g., balloons) placed distally of the treatment site.
It is desirable to place a distal protection device at a chosen location in order to achieve good sealing between the device and the wall of the vessel. Frequently it is necessary to match the protection device diameter with the vessel diameter, and vessels are known to taper or to have diameters that vary due to disease. It is also desirable to place the protection device in a relatively disease free portion of the vessel so as to minimize liberation of emboli from the wall of the vessel due to interaction with the protection device. Further, it is desirable that the device remains at the desired location during the procedure. Excessive motion of the wire or elongate guide member used to deliver the device can advance a protection device distally, beyond branch vessels, which thereby become unprotected from emboli.
Distal protection devices typically are mounted on a wire or tube that functions as a guidewire. As used herein, the term guidewire means either a traditional guidewire or other elongate member or hollow tube that is used in delivering the distal protection device. The protection device can be either a filter or an occlusive device such as a balloon. The distal protection devices are either fixedly attached to the guidewire or attached so as to permit a limited amount of motion between the device and the guidewire. Frequently, the same guidewire used to carry the device is also used to guide various catheters to and from the treatment site. For example, during the procedure, catheters may be exchanged over this guidewire. When catheters are exchanged inadvertent wire movement can cause the protection device to move within the vessel. Excessive wire motion can also retract a protection device proximally, where it can potentially become entangled in a stent or even be inadvertently removed from the vessel being protected. In some vessels, when guide catheters are repositioned, the protection device also tends to move within the vessel. This is undesirable because captured emboli can be released and/or new emboli can be formed distal to the protection device, blood vessels can be damaged, and/or the device can entangle with an implant such as a stent. Therefore, it is clear that too much movement of the device within the vessel could have catastrophic vessels.
Some work already has been done to provide for limiting the movement of a distal protection device or distal filter with respect to a guidewire. For example, a guidewire having a distal stop is described in WO 01/35857 (Tsugita et al.). The filter slides on the guidewire but cannot slide off the wire due to the distal stop. Another device which includes a slideable vascular filter having both distal and proximal sliding elements that move independently of each other over a mandrel is described in WO 01/21100 (Kusleika et al.) and is illustrated in FIG. 37. The device includes filter F, distal and proximal sliding elements (D and P) at either end of the filter, and stop S, all disposed about mandrel M. Body B of the filter F assumes a generally tabular shape and is made of a resilient material. The proximal length of the filter body has opening O therein. This opening permits body fluid with particulate therein, to enter the enclosure formed by body B of the filter. The mandrel is sufficiently flexible so that the device can be deployed in a curving body passageway. The distal-most length of the mandrel is shown having a flexible helically wound coil T thereover. This coil enhances the flexibility of the distal lip. The stop is at a fixed position on the mandrel and thus limits the movement of the sliding elements D and P. The filter is thus allowed to move along the mandrel or guidewire only the distance to the stop. While this system meets many of the needs in the art, it limits the range of motion of the filtration device on the guidewire, and the precision with which it can be placed is limited.
Another known limitation of distal protection devices relates to wire bias. It is well known that a guidewire will conform to the outside of a curved vessel on advancement of the wire in a distal direction and will conform to the interior of a curved vessel during retraction of the wire. Most distal protection devices are attached to wires, and when they are deployed in vessel curvature the wire bias will alternately move the device between the inside and the outside of the vessel curve. For filters this can defeat the protection effect by compressing the filter opening. For occlusion devices the wire bias effect can cause excessive motion of the occlusion device with potential liberation of embolic debris from the vicinity of the occlusive element.
Some work already has been done to provide for limiting the radial movement of a guidewire relative to a distal protection device. For example, a protection device having a proximal loop is described in EP 1,181,900 A2, (U.S. Ser. No. 09/628,212, Oslund et al.). A loop is provided proximal to the filter to immobilize the wire against the vessel wall regardless of wire bias. White this system meets many of the needs in the art, it adds bulk to the device and thereby limits crossing profile.
It would be desirable to have a distal protection system that can be precisely placed at a location within the vasculature and that can accommodate a wide range of axial and radial wire motion without disturbing the device's position.